現今，社會已步入高齡化的世代，人口老化讓醫師不得不面對身體機能衰退所帶來的各種疾病，其中骨質疏鬆症是常見的退化性疾病之一，而骨質疏鬆症患者可能發生壓迫性骨折的機率很高或有引發脊椎下背痛的問題，此類患者在治療上需要更為謹慎，是因為脊椎融合術所使用的椎弓根螺釘在骨質疏鬆症的椎骨上，椎弓根螺釘與椎骨之間的骨咬合能力大幅度下降，同時也增加椎弓根螺的鬆脫機率，因此椎弓根螺釘在骨質疏鬆症上的穩定性較差。
為了增加椎弓根螺釘與椎骨之間的骨咬合力，防止椎弓根螺釘鬆脫的問題發生，本研究使用LS-DYNA的有限元素分析模擬椎弓根螺釘在拔出過程中所發生的拔出強度，並對椎弓根螺釘類型(全圓錐型椎弓根螺釘、1/3圓錐型椎弓根螺釘、2/3圓錐型椎弓根螺釘和全圓柱型椎弓根螺釘)、椎弓根螺釘內徑(3.9 mm與4.9 mm)和人造假骨的密度(0.12 g/cm3、0.16 g/cm3、0.2 g/cm3以及0.32 g/cm3)進行分析，並且擁有圓錐型特徵的椎弓根螺釘會將骨擠壓現象考慮進去，探討有無骨擠壓現象是否會影響圓錐型椎弓根螺釘的拔出強度，而全圓柱型椎弓根螺釘則無骨壓現象存在。
本研究的結果顯示，在椎弓根螺釘的拔出模擬中，無骨擠壓現象的全圓錐型椎弓根螺釘的拔出強度是小於全圓柱型椎弓根螺釘，但加入骨擠壓現象後，全圓錐型椎弓根螺釘的拔出強度大幅度提升，其拔出強度大於全圓柱型椎弓根螺釘，而較小的椎弓根螺釘內徑可以獲得較大的拔出強度，並且與0.32 g/cm3骨密度相比，較低的骨密度所產生的拔出強度會減少。
本研究建立的數值模型是可預測各個椎弓根螺釘設計的拔出強度，其研究成果可以給予臨床醫師了解椎弓根螺釘的生物力學能力，以方便分析和選擇椎弓根螺釘的治療方案。

Pedicle screw fixation was widely used for the stabilization of the spine in a variety of spinal surgery, such as spine fusion surgery, the correction of deformity and the fixation of bone fracture, as spinal surgery in osteoporotic patients were increasingly common due to the aging of the population. Pedicle screw loosening was a common complication of spinal surgery, especially in osteoporotic patients. Because of lower bone density, the fixation between pedicle screw and bone was not stability. The effect of screw design on pullout strength associated with screw loosening was well studied in previous literatures and evaluated pedicle screw on biomechanical test by using finite element analysis. However, the linear elastic material model was difficult to reflect the failure of the bone.
This study aimed to develop a non-linear computational model using LS-DYNA to simulate the pullout force during the pullout process, and investigate the effect of pedicle screw types (fully conical pedicle screw, 1/3 cylindrical pedicle screw, 2/3 cylindrical pedicle screw and fully cylindrical pedicle screw), the core diameter of the pedicle screws (3.9 mm and 4.9 mm), the bone density (0.12 g/cm3, 0.16 g/cm3, 0.2 g/cm3 and 0.32 g/cm3) on pullout performance with the effect of bone compaction.
The results showed that the pullout force of the fully conical pedicle screw without bone compaction was lower than the fully cylindrical pedicle screw. The bone compaction effect improved the pullout force of the fully conical pedicle screw, and its pullout force was better than the fully cylindrical pedicle screw. The smaller core diameter of the pedicle screw had larger pullout force, and 0.32 g/cm3 caused more pullout force compared to less bone density.
The results could help surgeons to analyze the biomechanical ability of the pedicle screw and select the suitable device for orthopedic patients.

[1] Poole, K. E., & Compston, J. E. (2006). Osteoporosis and its management. Bmj, 333(7581), 1251-1256.
[2] Sözen, T., Özışık, L., & Başaran, N. Ç. (2017). An overview and management of osteoporosis. European journal of rheumatology, 4(1), 46.
[3] Chin, D. K., Park, J. Y., Yoon, Y. S., Kuh, S. U., Jin, B. H., Kim, K. S., & Cho, Y. E. (2007). Prevalence of osteoporosis in patients requiring spine surgery: incidence and significance of osteoporosis in spine disease. Osteoporosis international, 18(9), 1219-1224.
[4] Katonis, P., Christoforakis, J., Aligizakis, A. C., Papadopoulos, C., Sapkas, G., & Hadjipavlou, A. (2003). Complications and problems related to pedicle screw fixation of the spine. Clinical Orthopaedics and Related Research (1976-2007), 411, 86-94.
[5] Chen, C. S., Chen, W. J., Cheng, C. K., Jao, S. H. E., Chueh, S. C., & Wang, C. C. (2005). Failure analysis of broken pedicle screws on spinal instrumentation. Medical engineering & physics, 27(6), 487-496.
[6] Griza, S., de Andrade, C. E. C., Batista, W. W., Tentardini, E. K., & Strohaecker, T. R. (2012). Case study of Ti6Al4V pedicle screw failures due to geometric and microstructural aspects. Engineering Failure Analysis, 25, 133-143.
[7] Soshi, S., Shiba, R., Kondo, H., & Murota, K. (1991). An experimental study on transpedicular screw fixation in relation to osteoporosis of the lumbar spine. Spine, 16(11), 1335-1341.
[8] Halvorson, T. L., Kelley, L. A., Thomas, K. A., Whitecloud 3rd, T. S., & Cook, S. D. (1994). Effects of bone mineral density on pedicle screw fixation. Spine, 19(21), 2415-2420.
[9] Patel, P. S., Shepherd, D. E., & Hukins, D. W. (2010). The effect of screw insertion angle and thread type on the pullout strength of bone screws in normal and osteoporotic cancellous bone models. Medical engineering & physics, 32(8), 822-828.
[10] Zindrick, M. R., Wiltse, L. L., Widell, E. H., Thomas, J. C., Holland, W. R., Field, B. T., & Spencer, C. W. (1986). A biomechanical study of intrapeduncular screw fixation in the lumbosacral spine. Clin Orthop Relat Res, 203(203), 99-112.
[11] Mummaneni, P. V., Haddock, S. M., Liebschner, M. A., Keaveny, T. M., & Rosenberg, W. S. (2002). Biomechanical evaluation of a double-threaded pedicle screw in elderly vertebrae. Clinical Spine Surgery, 15(1), 64-68.
[12] Thompson, J. D., Benjamin, J. B., & Szivek, J. A. (1997). Pullout strengths of cannulated and noncannulated cancellous bone screws. Clinical Orthopaedics and Related Research®, 341, 241-249.
[13] Brasiliense, L. B., Lazaro, B. C., Reyes, P. M., Newcomb, A. G., Turner, J. L., Crandall, D. G., & Crawford, N. R. (2013). Characteristics of immediate and fatigue strength of a dual-threaded pedicle screw in cadaveric spines. The Spine Journal, 13(8), 947-956.
[14] Yaman, O., Demir, T., Arslan, A. K., Iyidiker, M. A., Tolunay, T., Camuscu, N., & Ulutas, M. (2015). The comparison of pullout strengths of various pedicle screw designs on synthetic foams and ovine vertebrae. Turkish Neurosurgery, 25(4).
[15] Patel, P. S., Shepherd, D. E., & Hukins, D. W. (2010). The effect of screw insertion angle and thread type on the pullout strength of bone screws in normal and osteoporotic cancellous bone models. Medical engineering & physics, 32(8), 822-828.
[16] Hsu, C. C., Chao, C. K., Wang, J. L., Hou, S. M., Tsai, Y. T., & Lin, J. (2005). Increase of pullout strength of spinal pedicle screws with conical core: biomechanical tests and finite element analyses. Journal of orthopaedic research, 23(4), 788-794.
[17] Chao, C. K., Hsu, C. C., Wang, J. L., & Lin, J. (2008). Increasing bending strength and pullout strength in conical pedicle screws: biomechanical tests and finite element analyses. Clinical Spine Surgery, 21(2), 130-138.
[18] Kang, S. H., Kim, K. T., Park, S. W., & Kim, Y. B. (2011). A case of pedicle screw loosening treated by modified transpedicular screw augmentation with polymethylmethacrylate. Journal of Korean Neurosurgical Society, 49(1), 75.
[19] 吳俊義;郭純琦；游美珠；黃慧貞；許瑋怡；周東賢；王慈娟；陳秀珍;陳昀佑；林淑玫(2016)。人體解剖學。華格那出版社。
[20] 脊椎的結構與功能, https://bonebro.com/spine-structuretest/.
[21] 認識骨質疏鬆症,
https://epaper.ntuh.gov.tw/health/201708/project_1.html.
[22] 骨質密度檢查, https://www.bones.nih.gov/health-info/bone/chinese.
[23] 台灣脊椎中心, http://taiwanspinecenter.com.tw/.
[24] 閻曉華脊骨神經醫學網,
https://reachbalance.blogspot.com/2008/04/scoliosis-04.html.
[25] Spineuniverse, https://www.spineuniverse.com/conditions/kyphosis.
[26] 骨科線上,
https://sites.google.com/view/bonenews/%E8%84%8A%E6%A4%8E%E9%86%AB%E5%AD%B8/spinal-instrumentation
[27] Inceoglu, S., Ferrara, L., & McLain, R. F. (2004). Pedicle screw fixation strength: pullout versus insertional torque. The spine journal, 4(5), 513-518.
[28] Krenn, M. H., Piotrowski, W. P., Penzkofer, R., & Augat, P. (2008). Influence of thread design on pedicle screw fixation. Journal of Neurosurgery: Spine, 9(1), 90-95.
[29] Kim, Y. Y., Choi, W. S., & Rhyu, K. W. (2012). Assessment of pedicle screw pullout strength based on various screw designs and bone densities—an ex vivo biomechanical study. The spine journal, 12(2), 164-168.
[30] Lill, C. A., Schlegel, U., Wahl, D., & Schneider, E. (2000). Comparison of the in vitro holding strengths of conical and cylindrical pedicle screws in a fully inserted setting and backed out 180. Clinical Spine Surgery, 13(3), 259-266.
[31] Abshire, B. B., McLain, R. F., Valdevit, A., & Kambic, H. E. (2001). Characteristics of pullout failure in conical and cylindrical pedicle screws after full insertion and back-out. The Spine Journal, 1(6), 408-414.
[32] Lill, C. A., Schneider, E., Goldhahn, J., Haslemann, A., & Zeifang, F. (2006). Mechanical performance of cylindrical and dual core pedicle screws in calf and human vertebrae. Archives of orthopaedic and trauma surgery, 126(10), 686-694.
[33] Thompson, M. S., McCarthy, I. D., Lidgren, L., & Ryd, L. (2003). Compressive and shear properties of commercially available polyurethane foams. Journal of biomechanical engineering, 125(5), 732-734.
[34] Yao, Y., Yuan, H., Huang, H., Liu, J., Wang, L., & Fan, Y. (2021). Biomechanical design and analysis of auxetic pedicle screw to resist loosening. Computers in Biology and Medicine, 133, 104386.
[35] Kelly, N., & McGarry, J. P. (2012). Experimental and numerical characterisation of the elasto-plastic properties of bovine trabecular bone and a trabecular bone analogue. Journal of the mechanical behavior of biomedical materials, 9, 184-197.
[36] Liu, C. L., Chen, H. H., Cheng, C. K., Kao, H. C., & Lo, W. H. (1998). Biomechanical evaluation of a new anterior spinal implant. Clinical biomechanics, 13(1), S40-S45.
[37] Belda, R., Palomar, M., Marco, M., Vercher-Martínez, A., & Giner, E. (2021). Open cell polyurethane foam compression failure characterization and its relationship to morphometry. Materials Science and Engineering: C, 120, 111754.
[38] Tsai, W. C., Chen, P. Q., Lu, T. W., Wu, S. S., Shih, K. S., & Lin, S. C. (2009). Comparison and prediction of pullout strength of conical and cylindrical pedicle screws within synthetic bone. BMC musculoskeletal disorders, 10(1), 1-9.
[39] Stölken, J. S., & Kinney, J. H. (2003). On the importance of geometric nonlinearity in finite-element simulations of trabecular bone failure. Bone, 33(4), 494-504.
[40] Mercer, C., He, M. Y., Wang, R., & Evans, A. G. (2006). Mechanisms governing the inelastic deformation of cortical bone and application to trabecular bone. Acta Biomaterialia, 2(1), 59-68.
[41] Van Rietbergen, B., Odgaard, A., Kabel, J., & Huiskes, R. (1998). Relationships between bone morphology and bone elastic properties can be accurately quantified using high‐resolution computer reconstructions. Journal of Orthopaedic Research, 16(1), 23-28.
[42] Niebur, G. L., Feldstein, M. J., Yuen, J. C., Chen, T. J., & Keaveny, T. M. (2000). High-resolution finite element models with tissue strength asymmetry accurately predict failure of trabecular bone. Journal of biomechanics, 33(12), 1575-1583.
[43] Bayraktar, H. H., Morgan, E. F., Niebur, G. L., Morris, G. E., Wong, E. K., & Keaveny, T. M. (2004). Comparison of the elastic and yield properties of human femoral trabecular and cortical bone tissue. Journal of biomechanics, 37(1), 27-35.
[44] Reilly, D. T., & Burstein, A. H. (1975). The elastic and ultimate properties of compact bone tissue. Journal of biomechanics, 8(6), 393-405.
[45] Mullins, L. P., Bruzzi, M. S., & McHugh, P. E. (2009). Calibration of a constitutive model for the post-yield behaviour of cortical bone. Journal of the Mechanical Behavior of Biomedical Materials, 2(5), 460-470.
[46] Yao, Y., Wang, L., Li, J., Tian, S., Zhang, M., & Fan, Y. (2020). A novel auxetic structure based bone screw design: Tensile mechanical characterization and pullout fixation strength evaluation. Materials & design, 188, 108424.
[47] Dickman, C. A., Fessler, R. G., MacMillan, M., & Haid, R. W. (1992). Transpedicular screw-rod fixation of the lumbar spine: operative technique and outcome in 104 cases. Journal of neurosurgery, 77(6), 860-870.
[48] Lonstein, J. E., Denis, F., Perra, J. H., Pinto, M. R., Smith, M. D., & Winter, R. B. (1999). Complications associated with pedicle screws. JBJS, 81(11), 1519-28.
[49] DeWald, C. J., & Stanley, T. (2006). Instrumentation-related complications of multilevel fusions for adult spinal deformity patients over age 65: surgical considerations and treatment options in patients with poor bone quality. Spine, 31(19S), S144-S151.
[50] Cho, W., Shimer, A. L., & Shen, F. H. (2011, June). Complications associated with posterior lumbar surgery. In Seminars in Spine Surgery (Vol. 23, No. 2, pp. 101-113). WB Saunders.
[51] Eysel, P., Schwitalle, M., Oberstein, A., Rompe, J. D., Hopf, C., & Küllmer, K. (1998). Preoperative estimation of screw fixation strength in vertebral bodies. Spine, 23(2), 174-180.
[52] Battula, S., Schoenfeld, A. J., Sahai, V., Vrabec, G. A., Tank, J., & Njus, G. O. (2008). The effect of pilot hole size on the insertion torque and pullout strength of self-tapping cortical bone screws in osteoporotic bone. Journal of Trauma and Acute Care Surgery, 64(4), 990-995.